1. Field of the Invention
The present invention relates to a web coating apparatus, and more particularly to coating material supply systems and methods for web coating apparatuses used in the printing industry.
2. Description of Related Art
In web coating apparatuses, a coating and drum is partially submerged in a tray of coating material. The coating drum rotates and the coating material is deposited from a surface of the coating drum to the web passing there over. A level detector having two electrodes senses when the level of coating material in the tray reaches predetermined levels. As the drum deposits coating material on the web, the quantity of coating material in the tray is depleted. When the quantity of coating material in the tray is depleted such that the level drops below the predetermined point, a pump draws a coating material from a coating reservoir and deposits the coating material into the tray. When the pump deposits sufficient quantity of the coating fluid into the tray to bring the level of coating fluid in the tray up to the predetermined level, the sensor senses the existence of the coating fluid at the predetermined level and shuts off the coating supply pump.
There are a few drawbacks of this technique. One drawback is that coating or printing quality may change due to varying levels of coating material in the transfer pan. Furthermore, since the coating material is exposed to air in the transfer pan, its viscosity may change over time resulting in varying coating or printing quality. Thus, there is a need for a system that can accurately control the level of coating material in the transfer pan and further disallow the coating material from significantly changing viscosity over time.
The present exemplary embodiments of the present invention provide a coating material supply system which may accurately control the level of coating material in a transfer pan of a coating tower of a printing system. An exemplary embodiment may both provide and remove coating material, such as UV coatings, aqueous varnishes, inks, or other fluids, to and from a transfer tray or chamber in order to maintain a substantially uniform level, pressure, temperature, or viscosity of the coating material.
An exemplary web coating apparatus that provides coating material which coats a web material as it moves past a coating drum includes a transfer pan or chamber for holding coating material that is being transferred from the transfer pan to the coating drum. The coating drum is partially submerged in the coating material. A coating supply system provides and removes coating material from the transfer pan. An ultrasonic level sensor measures the coating material level in the transfer pan and provides information to the coating supply system so that coating material is being supplied and removed from the transfer pan at rates that keeps the level of coating material in the transfer pan substantially unchanging.
The continuous supply and removal of coating material from the transfer pan also aids in keeping the viscosity and temperature of the coating material more uniform during a printing or coating process.